Brake device for an elevator with monitoring capabilities

ABSTRACT

An elevator drive has a brake device with compression springs to actuate brake levers, and brake linings on a brake drum creating a braking force. A sensor is provided to detect the movement of a brake magnet armature tappet. A bracket is attached to the brake magnet tappet on one end and a distance piece carrying the sensor housing is arranged on the other end. A restoring lug is attached to the existing mechanical indicator. A monitor evaluates the sensor signal and turns off the elevator drive in the event of dangerous operational states via a safety circuit. The system allows the state of the brake device to be monitored. The more the brake linings wear off due to abrasion, the smaller the distance between the armature and the brake magnet housing. If the armature is in contact with the brake magnet housing, the braking ability of the brake linings is completely void.

The present application is a continuation of PCT/EP2008/055303 filedApr. 30, 2008.

The invention relates to a device and a method for monitoring a brakedevice for an elevator drive consisting of brake levers with compressionsprings which exert on the latter a spring force, whereby brake liningscause a braking force on a brake drum and at least one brake magnetlifts the brake levers against the spring force.

BACKGROUND OF THE INVENTION

From patent specification EP 1 156 008 B1 a brake device for a drivemachine has become known. The brake device consists of a first brakelever and a second brake lever, arranged on each of which is a brakeshoe that acts on a brake drum. At their lower ends the brake levers aresupported in swivel bearings on a bearing pedestal and at their upperends guided on a bar. For the purpose of actuating the brake shoes, acompression spring is provided for each brake lever. For the purpose oflifting the brake shoes, provided on each brake lever is a magnet whichacts against the compression spring. The magnets are arranged on a framewhich is joined to the bearing pedestal. Arranged on the inside of eachmagnet support is a microswitch. A tappet of the microswitch is actuatedby means of a cam that is arranged on a plunger disk. The switchingstatus of the microswitch indicates to the control of the elevatorwhether by means of the magnets the brake is released or lifted, orwhether the brake is not released or not lifted.

The present invention provides a device and a method for a safely actingbrake device which prevents states that are dangerous for the users ofthe elevator.

The main advantages derived from the invention are that not only, ashitherto, is the end-position of the brake levers in the released stateas brought about by the brake magnet monitored, but also the position ofthe movable brake-magnet part, such as the brake-magnet tappet, and ofthe plunger of the brake magnet. By this means it is possible to avoidthe movable brake-magnet part such as, for example, the brake-magnettappet or brake magnet plunger coming into contact with the fixedbrake-magnet part such as, for example, the brake-magnet housing,through gradual abrasion of the brake linings and thereby reducing, orin the extreme case eliminating, the braking capacity of the brakedevice. The elevator drive can hence be directly switched off before thebrake fails, or before a state that is dangerous for the users of theelevator can occur.

A further advantage is the simple construction of the device accordingto the invention, which can be realized by means of, for example, theuse of a variety of sensors, such as a sensor proximity switch, linearemitter, etc.

With the invention, an elevator drive can be advantageously constructedand also an existing elevator drive advantageously retrofitted. Thesensor can be arranged in the fixed brake-magnet part as, for example,inside or outside the brake magnet housing, in either case the relativemovement of the movable brake part as, for example, the brake-magnettappet or the plunger, relative to the fixed brake-magnet part as, forexample, the brake-magnet housing, being registered.

With the simple construction of the position monitor, existing elevatorsystems can be retrofitted with the position monitor according to theinvention without great outlay, for example by mounting the sensor onthe brake-magnet tappet.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with the foregoing purposes and advantages, an elevatordrive according to the invention has a brake device with brake levers towhich a spring force is applied by means of compression springs. Brakelinings cause a braking force on a brake drum, and at least one brakemagnet lifts the brake levers against the spring force. At least onesensor is provided that monitors a movement or a distance between aplunger of the brake magnet and a brake magnet housing. With the sensorsignal, not only a signal for the end-position of the brake magnettappet or brake magnet plunger can be generated, but also furthersignals as, for example, a signal for brake travel, a signal for brakelining wear, or a signal for brake drum heating. The safety for theelevator users can thereby be additionally increased, since theoperating states of the brake device that lead to dangerous situationsare promptly recognizable.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in more detail by reference to theattached figures wherein

FIG. 1 is a diagrammatic illustration of an elevator drive with a brakedevice with two compression springs and a brake magnet;

FIG. 2 is a diagrammatic illustration of an elevator drive with a brakedevice with a double brake magnet;

FIG. 3 is an illustration of variant embodiment of an elevator drivewith a brake device with a compression spring and a brake magnet,

FIG. 4 is a detail illustration of a connection of a brake-magnet tappetwith a brake lever;

FIG. 5 is a diagrammatic illustration of a sensor for registering amovement or a distance;

FIGS. 6 and 6 a are perspective detail views of alternative arrangementsof the sensor on the brake-magnet tappet;

FIGS. 6 b and 6 c are perspective detail views of a spring-returningvane;

FIGS. 7 and 7 a are graphs depicting an output signal of the sensor asit depends on the distance registered; and

FIG. 8 is a block circuit diagram of a monitor for evaluating the sensorsignal and for indicating the state of the brake device.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows diagrammatically a brake device 1 with a first compressionspring 2, a second compression spring 3, a first brake lever 5, a secondbrake lever 6, and a brake magnet 4. The first compression spring 2exerts a spring force on the first brake lever 5. The second compressionspring 3 exerts a spring force on the second brake lever 6. The firstcompression spring 2 is guided by means of a first bar 7 which at oneend is joined to a machine housing 8 and at the other end has a firstadjusting element 9, for example nuts with locknuts mounted on threadsof the bar 7, the braking force and the opening of the first brake lever5 being settable with the adjusting element 9. This second compressionspring 3 is guided by means of a second bar 10 which at one end isjoined to the machine housing 8 and at the other end has a secondadjusting element 11, for example nuts with locknuts mounted on threadsof the bar 10, the braking force and the opening of the second brakelever 6 being settable with the adjusting element 11. Arranged on thefirst brake lever 5 is a first brake shoe 12 that carries a first brakelining 13, the first brake lining 13 creating a braking force on a brakedrum 14. Arranged on the second brake lever 6 is a second brake shoe 15that carries a second brake lining 16, the second brake lining 16creating a braking force on the brake drum 14. The first brake lever 5is mounted in swiveling manner on a first lever axle 17 that issupported on the machine housing 8. The second brake lever 6 is mountedin swiveling manner on a second lever axle 18 that is supported on themachine housing 8. The brake drum 14 is usually joined to a motor axlethat is not shown.

The brake magnet 4 consists of a magnet coil 20 which is arranged in afixed brake-magnet part as, for example, a brake-magnet housing 19which, when carrying electric current, acts through its magnetic fieldon a movable brake-magnet part such as, for example, a plunger 21. Thebrake-magnet housing 19 with the magnet coil 20 and the plunger 21 repeleach other and act against the spring forces of the compression springs2, 3. The movable brake-magnet part executes a relative movementrelative to the fixed brake-magnet part. At a first joint 22, thebrake-magnet housing 19 is connected to the first brake lever 5. Theplunger 21 is connected to a brake-magnet tappet 23 which in turn, at asecond joint 24, is connected with a third bar 25. By means of thirdadjustment elements 26, the third bar 25 is connected to the secondbrake lever 6.

The more the brake linings 13, 16 wear due to abrasion, the smaller thedistance d of the plunger 21 from the brake-magnet housing 19 becomes.Should the plunger 21 rest against the brake magnet housing, the brakingcapacity of the brake linings 13, 16 is completely eliminated. So thatthis operating state that is dangerous for elevator users cannot occur,at least one sensor 27 is provided that detects the movement or thedistance d. Sensor 27 can be, for example, a proximity switch, forexample with analog output, or a linear emitter. The sensor 27 can bearranged on the plunger 21 and register the distance d from thebrake-magnet housing 19. The sensor 27 can also be arranged on thebrake-magnet housing 19 and register the distance d from the plunger 21.The sensor 27 can also be arranged on the brake-magnet tappet 23 andexecute the relative movement of the brake-magnet tappet 23 relative tothe brake-magnet housing 19, the sensor 27 registering the relativeposition of the brake-magnet tappet 23 relative to the brake-magnethousing 19. Details are explained more fully in FIGS. 4 to 6. The sensorarrangement according to FIGS. 4 to 6 is preferred for retrofitting inexisting elevator installations. For new installations, a sensorarrangement according to FIGS. 4 to 6, or a brake magnet 4 with abuilt-in sensor 27, can be used.

FIG. 2 shows diagrammatically a brake device 1 with a double brakemagnet 4 consisting of a first magnet coil 20.1, a second magnet coil20.2, a first plunger 21.1, a second plunger 21.2, a first brake-magnettappet 23.1, and a second brake-magnet tappet 23.2. The firstbrake-magnet tappet 23.1 is connected in swiveling manner (joint 22.1)to the first brake lever 5. The second brake-magnet tappet 23.2 isconnected in swiveling manner (joint 22.2) to the second brake lever 6.The brake-magnet housing 19 is joined to the machine housing 8. A firstsensor 27.1 monitors, or registers, the movement or the distance dlbetween the first plunger 21.1 and the brake-magnet housing 19. A secondsensor 27,2 monitors, or registers, the movement or the distance d2between the second plunger 21.2 and the brake-magnet housing 19. Thefirst sensor 27.1 can also be arranged on the swivel joint 22.1. Thesecond sensor 27.2 can also be arranged on the swivel joint 22.2.

FIG. 3 shows a variant embodiment of a brake device 1 with only onecompression spring 2 and one brake magnet 4. The compression spring 2rests against the second brake lever 6 and against a fourth bar 28 whichat its other end is connected to the first brake lever 5. Thecompression spring 3 thus exerts a spring force on both brake linings13, 16. The brake magnet 4 functions as explained in FIG. 1, it beingpossible for at least one sensor 27 to be built into the brake magnet 4or, as shown in FIGS. 4 to 6, mounted on the second swivel joint 24. Thebrake magnet 4 acts against the spring force of the compression spring 3and releases the brake linings 13, 16 from the brake drum 14. The forceof the brake magnet 4 can also be created manually by means of abrake-release lever 29. A fifth bar 32 limits the displacement of thebrake levers 5, 6 by the magnet 4 or by the brake-release lever 29.Arranged on a gear output shaft 31, and referenced with 30, is atraction sheave over which suspension and traction means of the elevatorcar and of the counterweight are guided.

FIG. 4 shows details of the connection of the brake-magnet tappet 23with the second brake lever 6. By means of a pin 33 that penetratesthrough the brake-magnet tappet 23, the third bar 25 is connected inswiveling manner to the brake-magnet tappet 23, spring rings 38 securingthe pin at both ends. The end 37 of the brake-magnet tappet 23 may befork-shaped. Provided at the free end of the third bar 25 is a thread 34which, together with nuts 35, serves as third adjusting element 26. Atleast one brake lever switch 40 can be provided to monitor whether thebrake levers 5, 6, and thus the brake linings 13, 16, have been releasedfrom the brake drum 14.

As shown in FIG. 4, the brake-lever switch 40 can monitor the positionof the brake lever 6, or be arranged in such manner that the formermonitors the position of the pin 33 relative to the brake-magnet housing19. Normally arranged on the brake-magnet housing 19 is a sixth bar 41,provided on which is a first vane 42. With the relative position of thepin 33 relative to the first vane 42, the distance of the plunger 21from the brake-magnet housing 19 can be determined. The sixth bar 41together with the first vane 42 is also referred to as a “mechanicalindicator”. The more the brake linings 13, 16 wear through abrasion, theless the pin 33 is distant from the first vane 42. As shown in FIG. 6,in the present exemplary embodiment the sixth bar 41 and the pin 33 areused as a mechanical reference point for the sensor 27.

FIG. 5 shows diagramatically the sensor 27 for registering the movementor the distance d of the plunger 21 from the brake-magnet housing 19, orthe relative movement of the brake-magnet tappet 23 relative to thebrake-magnet housing 19. In the present exemplary embodiment, providedas sensor 27 is an inductive proximity switch with an analog outputwhich responds to ferromagnetic objects. The sensor 27 has a sensorhousing 43 with a second thread 44 onto which a locking nut 45 can bescrewed. The sensor housing 43 is screwed into a magnetically neutraldistance piece 46 of, for example, plastic, and by means of the lockingnut 45 secured against turning, the distance piece 46 on the end-face 47of the sensor 27 having a defined wall thickness 48, for example 1 mm.Referenced with 49 is an air gap between a second vane 50 and thedistance piece 46. Wall thickness 48 plus air gap 49 yields the sensorgap 51 from the second vane 50. In FIG. 7 and in FIG. 7 a the sensor gap51 is referenced as “s.” With the distance piece 46, setting work onsite is avoided. As shown in FIG. 6 and in FIG. 6 a, the distance piece46 serves also as a support for the sensor 27. The sensor 27 can at thefactory be completely screwed into the distance piece 46 and installedon site without settings in the axial direction. Power supply to thesensor 27, and the signal output of the sensor 27, take place via aconnecting cable 52.

FIG. 6, FIG. 6 a show details of arrangements of the sensor 27 on thebrake-magnet tappet 23. A stirrup 53 is fastened onto one end of theexisting pin 33, and arranged on the other end is the distance piece 46that bears the sensor housing 43. In FIG. 6, with the aid of elongatedslots 54 and screws 55, the distance piece 46 can be alignedperpendicular to the direction of movement of the brake-magnet tappet 23on the exisiting sixth bar 41. The second vane 50 is fastened to thesixth bar 41. A setting of the brake-magnet tappet 23 in the directionof movement is not necessary.

In FIG. 6 a, the stirrup 53 is fastened by means of screws 55 a to thefork-shaped end 37 of the brake-magnet tappet 23. As shown in FIG. 6 a,the second vane 50 is arranged coaxial to the axis of the sixth bar 41and of the sensor 27. The second vane 50 is embodied in aspring-returning manner.

By this means it is possible to avoid the suffering of damages by sensor27 and/or the vane 50 should a collision occur between the sensor 27 andthe second vane 50, either because of incorrect mechanical settings orbecause of a travel of the brake magnet 4 that deviates from the norm.

FIGS. 6 b and 6 c show details of the second vane 50. A cylindrical basebody 50.1 is connected with the sixth bar 41 and serves as a support forguides 50.2 which slide along pins 50.6 of a cap 50.3 with disk 50.4. Aspring 50.5 rests at one end on the base body 50.1 and at the other endon the disk 50.4 and holds the cap 50.3 with the disk 50.4 in theend-position shown in FIGS. 6 a and 6 c. In the case of a collision ofthe sensor 27 with the vane 50, the cap 50.3 with the disk 50.4 is movedagainst the spring force of the compression spring 50.5.

FIG. 7, FIG. 7 a show the output signal of the sensor 27 as it dependson the registered distance, sensor gap 51, or relative movement of thebrake magnet tappet 33 relative to the brake-magnet housing 19. Thevarying distance of the end-face 47 of the sensor 27 from the secondvane 50 is referenced in FIG. 7, FIG. 7 a as “s.” The proximity switchwith analog output that is used as sensor 27 may have a current outputbetween 0 and 20 mA, which is robust against electromagneticinterference signals as shown in FIG. 7, or a current output signalbetween 0 and 5 mA as shown in FIG. 7 a at a sensor gap 51, or s, ofbetween 0 and 10 mm. FIG. 7, FIG. 7 a show the characteristic of thecurrent I as a function of the travel s or of the sensor gap 51. Ofinterest is the linear area of the curve between 8 mA and 17 mA as shownin FIG. 7, or between 2 mA and 4.3 mA as shown in FIG. 7 a, and a sensorgap 51, or s, between 3 mm and 7.5 mm. The analog current output signalis fed to an analog/digital converter 64 of a monitor 60 that is shownin FIG. 8 and by which it is evaluated.

On elevators with many short trips and/or that stop at many floors, thebrake linings 13, 16 can wear more quickly than usual. Elevators thatare halted by the brake in the area of the story (so-called two-speedelevators), have higher wear of the brake linings. A defective state ofthe brake can be promptly deduced from the diminishing leveling accuracyof the elevator car on the story. With drives with releveling, theleveling accuracy is always the same, and a defective state of the brakedoes not manifest itself visibly.

A further cause of excessive wear of the brake linings 13, 14 can be anat least partial failure of the magnet coil 20, as a consequence ofwhich the magnet coil 20 no longer produces the full force for releasingthe brake lever 5, 6, and the motor moves the traction sheave 30 withclosed brake levers 5, 6. As shown in FIG. 4, to avoid this state withthe resultant excessive wear of the brake linings 13, 16, a brake-leverswitch 40 is provided which monitors the position of the brake levers 5,6 when the brake is perceived by the elevator control to be lifted, anddetermines whether on a travel command the brake levers 5, 6, and thusthe brake linings 13, 16, have been released from the brake drum 14.Should the brake-lever switch 40 not be present, or not supported by theelevator control, travel without lifted brake cannot be avoided, but themonitor 60 nonetheless detects and prevents a total failure of thebrake.

FIG. 8 shows a block circuit diagram of the monitor 60 for analyzing thesensor signal of the sensor 27 and for indicating the state of the brakedevice 1. A processor 61 of the monitor 60 operates according to aprogram that is stored in a program memory 62, the processor placingdata into a working memory 63 or fetching it from thence. The analogsensor signal of the sensor 27 is fed to the analog/digital converter 64of the monitor 60. Converter 64, memory 63, memory 62, and the processor61 communicate via a bus system 65. By means of a diagnosis instrument66, the program or parameters can be modified or data read out. A firstpower-supply device 67 supplies the monitor 60 with electrical energy,for example with a voltage of 5 V. The first power-supply device 67 issupplied by a monitor-external second power-supply device 68, forexample with alternating voltage from the power supply network at 220 Vor, for example, with direct voltage at 24 V from the not-shown elevatorcontrol.

Depending on the sensor signal of the sensor 27, a relay 69 istriggered. In the normal operating state of the brake device 1, therelay 69 is activated and a potential-free contact 70 that belongs tothe relay 69 is closed. To visualize the state of the closed contact, afirst indicator 71, for example a green-lit LED, can be provided. In thesafety circuit 72 of the not-shown elevator control, the potential-freecontact 70 is connected in series. A second potential-free contact canalso be connected in series, and on failure of the relay 69 the safetycircuit can be opened by means of the second potential-freerelay-operable contact. The safety circuit of the elevator control is aseries circuit of contacts that monitor important functions of theelevator operation as, for example, doors closed, brake lifted, normalspeed of the elevator car, normal load, etc., and if at least onecontact is open no car travel is executed.

Depending on the sensor signal of the sensor 27, different operatingstates are detected and indicated. The normal operating state is madevisible by means of a second indicator 73, for example by means of agreen-lit LED. The operating state corresponding to excessively wornbrake linings 13, 16 is made visible by means of a third indicator 74,for example by means of a red-lit LED. A further operating state thatcorresponds to the stroke of the brake device 1 or of the brake-magnettappet 23 is visualized by means of a fourth indicator 75, for exampleby means of a red-lit LED. A further operating state corresponding toheating of the brake drum 14 is visualized by means of a fifth indicator76, for example by means of a red-lit LED. A further operating statecorresponding to a failure detected by electronic tests is visualized bymeans of a sixth display 77, for example by means of a red-lit LED. Afurther operating state of the brake corresponding to the closedposition, or to the open position, of the brake levers 5, 6 isvisualized by means of a seventh indicator 79, for example by means ofan orange-lit LED. The monitor 60 can be equipped with all, or with aselection of, the said indicators.

With a push-button 78, on electronic initialization of the monitor 60,measurement values of the sensor 27 that were saved in the non-volatileworking memory 63 (EEPROM) can be reset. After mechanical setting workon the brake device 1, the push-button 78 must be pressed. For example,the processor 61 calculates the mean value of a plurality of measurementvalues of the sensor signal for the closed position of the brake levers5, 6, or for the brake that has been activated by means of compressionsprings 2, 3, and the mean value of a plurality of measurement values ofthe sensor signal for the open position of the brake levers 5, 6, or ofthe brake levers 5, 6 that have been lifted by means of the brake magnet4. After resetting of the mean values, mean values of new measurementvalues are calculated and saved.

The sixth bar 41 with the first vane 42 and the tappet pin 33 are usedas mechanical reference point for the sensor 27, there being provided assensor gap 51, for example, 3 mm, or as air gap 49, 2 mm. As shown inFIG. 7, at 3 mm sensor gap 51 the linear area of the sensor signal, orof the output current I, begins. With an air gap 49 of 2 mm, collisionof the sensor 27 with the second vane 50 can normally also be avoided atmaximum wear of the brake linings 13, 16.

In normal operation with closed position of the brake levers 5, 6 andwith open position of the brake levers 5, 6, the sensor gap 51 in thepresent exemplary embodiment is greater than 3 mm. In the closedposition of the brake levers 5, 6, the sensor gap 51 is given.Deviations are caused by wear of the brake linings 13, 16 or by heatingof the brake drum 14. The monitor 60 can differentiate between thedeviations. As the brake linings 13, 14 wear, the brake-magnet tappet 23moves relative to the brake-magnet housing 19. On heating of the brakedrum 14, the brake magnet tappet 23 moves relatively away from thebrake-magnet housing 19.

Based on the analog/digital transformed sensor signal, the processor 61of the monitor 60 calculates the speed and the direction of the brakemagnet tappet 23. To determine the closed position and the open positionof the brake levers 5, 6, signal values or measurement values areallocated to the corresponding position if the brake-magnet tappet 23does not, for example, move more than 0.01 mm in 100 ms. For the closedposition, a sensor gap 51 of, for example, between 3 m and 5.5 mm ispossible, and for the open position, for example, a sensor gap 51 ofbetween 5 mm and 7.5 mm is possible.

With each car travel the speed and the direction of the brake-magnettappet 23 changes, whereby the number of trips is detected and saved inthe working memory 63.

During the first, for example, 8 trips, the indicator 73 flashes at, forexample, 10 Hz, with, for example, 8 signal values of the sensor 27, ormeasurement values, being assigned to the corresponding closed positionor open position and therefrom the corresponding mean values formed andsaved in the working memory 63. The closed position and open positionlearned on the brake device 1 serve as a starting point for theoperating state of excessive wear of the brake linings 13, 16 or for theoperating state of excessive heating of the brake drum 14. Thereafter,the second indicator 73 flashes at, for example, 1 Hz and indicates afully functional capability of the brake device 1. Monitoring of theclosed position and of the open position can be continued. Should themean values of the measured signal values deviate by more than, forexample, 0.5 mm, the saved mean values are overwritten with the currentmean values. Alternatively, the aforementioned closed position and openposition can be learned once only with a plurality of measurementvalues.

With increasing wear of the brake linings 13, 16, for example 0.5 mmbefore the critical point, the third indicator 74, is switched on andswitched off with, for example, a frequency of 10 Hz. On attaining thecritical point (sensor gap 51=3 mm), the relay 69 is switched off with atime delay and the potential-free contact 70 is opened. The time delayis of such magnitude that the elevator car can complete the current tripand the transported persons can leave the elevator car. The operatingstate of excessive wear of the brake linings 13, 16 is then signaledwith the continuously switched-on third indicator 74.

Should the stroke or distance between the closed position and the openposition be smaller than, for example, 2 mm during, for example, 3seconds, the monitor 60 assumes a fault, for example an incorrectmechanical setting or a mechanical blocking. A further fault that can bedetected from the stroke is the number of open positions in relation tothe maximum travel time of the elevator car. On occurrence of a strokefault, the relay 69 is switched off with a time delay and thepotential-free contact 70 is opened. The time delay is of such magnitudethat the elevator car can complete the current trip and the transportedpersons can leave the elevator car. The fourth indicator 75 isinitially, for example, switched on and switched off with a frequency of10 Hz and then continuously switched on.

If, due to failure of the brake magnet, or due to software faults, ordue to hardware faults in the electronic switching circuits, the brakedevice 1 is not lifted, or if the brake linings 13, 16 are not releasedfrom the brake drum 14, the monitor 60 can also not detect a strokefault. In the case of car travel with a closed brake, the brake drum 14and the brake linings 13, 16 heat. Upon heating, brake drum 14 and brakelinings 13, 16 expand and cause a movement of the brake-magnet tappet 23relative to the brake-magnet housing 19 opposite in direction to themovement caused by wear. The deviation is evaluated in relation to thedistance of the closed position from the critical point. The moreadvanced the wear of the brake linings 13, 16 is, or the thinner thebrake linings 13, 14 are, the smaller is the deviation that causesswitching-off. The deviation can lie in the range of, for example, 0.7mm to 1.5 mm. On occurrence of an impermissible deviation, the relay 69is switched off with time delay and the potential-free contact 70 isopened. The time delay is of such magnitude that the elevator car cancomplete the current trip and the transported persons can leave theelevator car. The fifth indicator 76 is initially switched on and offwith a frequency of 10 Hz and then switched on continuously.

The monitor 60 itself can also prevent switching-on of the relay 69 oreffect switching-off of the relay 69 and an opening of thepotential-free contact 70. Reasons therefor are negative plausibilitytests during electronic initiation or operation of the monitor 60.Further reasons for switching-off are a missing sensor 27, or a brakedevice 1 which has not been lifted for a long period of time, forexample three months. This type of fault is visualized by means of thesixth indicator 77.

1. A monitorable brake device for an elevator drive, the brake devicecomprising at least one compression spring which exerts a spring forceon brake levers, brake linings for exerting a braking force on a brakedrum and a brake magnet for lifting the brake levers against the springforce, a brake-magnet housing joined to a first brake-lever, abrake-magnet part being movable relative to the brake-magnet housing andjoined to a second brake lever, and a sensor for providing a monitorableoutput proportional to an extent of relative movement of the movablebrake-magnet part relative to the brake magnet housing.
 2. The brakedevice according to claim 1, wherein the movable brake-magnet part has abrake-magnet tappet, the sensor being mounted to the tappet andpositioned whereby the output corresponds to relative movement of thebrake-magnet tappet relative to the brake-magnet housing.
 3. The brakedevice according to claim 1, wherein the brake magnet has a plunger, thesensor being mounted to the plunger and positioned such that the outputcorresponds to movement of the plunger.
 4. The brake device according toclaim 1, wherein the fixed brake-magnet part is a brake-magnet housing,the sensor being mounted to the brake-magnet housing.
 5. The brakedevice according to claim 2, wherein the brake-magnet tappet has atransverse pin, the sensor being mounted to the pin, the brake devicefurther having a mechanical indicator to which a second vane is mountedfor indicating the position of the pin relative to the brake-magnethousing, the sensor output corresponding to the position of the pin. 6.The brake device according to claim 5, wherein the second vane has aspring-returning housing.
 7. The brake device according to claim 1,wherein the sensor is an inductive proximity switch with an analogoutput.
 8. The brake device according to claim 1, further comprising amonitor for receipt of the sensor signal having means for detecting andindicating different operating states of the brake device dependent uponthe sensor signal received.
 9. An elevator with an elevator drive with abrake device according to claim
 1. 10. A method for retrofitting anelevator drive with a brake device consisting of brake levers withcompression springs that exert on the levers a spring force, whereinbrake linings cause a braking force on a brake drum and at least onebrake magnet lifts the brake levers against the spring force, comprisingthe steps of: mounting at least one sensor on a brake-magnet tappet of amovable brake-magnet part; and generating a sensor output correspondingto relative movement of the brake-magnet tappet relative to a fixedbrake magnet part.
 11. The brake device of claim 1, further including amonitor coupled to the sensor having indicators for visually displayinga plurality of states of the brake device, the states including: anormal operating state; an excessive wear state of brake linings; astate indicating brake magnet stroke condition; a state of brake drumheating; and a state reflecting failure of an electronic test.
 12. Thebrake device of claim 1, further including a monitor having a processorcoupled to the sensor for utilizing sensor output to determine meanreference values for closed and open positions of the brake levers andfor comparing the reference values to sensor output during subsequentbrake operation to determine an operating state of the brake device. 13.The brake device of claim 12 wherein the processor further includesmeans for determining speed and duration of the relative movement of themovable brake-magnet part relative to the brake magnet housing fordetermining an operating state of the brake device.